Alkylpolyamine-modified cyanide copper plating bath



Nov. 12, 1957 B. D. osTRow 2313,056

ALKYLPOLYAMINE MODIFIED CYANIDE COPPR PLATING BATH Filed Nov. 14, 1955 2Sheets-Shee: l

Nov. 12, 1957 B. D. OSTROW 2,813,066

ALKYLPOLYAMINE MODIFIED .CYANIDE COPPER PLATING BATH Filed Nov. 14, 19552 Sheets-Sheet 2 INVENTOR( ai i/K? D. Offd United States Patents O"ALKYLPOLYAMINE-MODIFIED CYANIDE COPPER PLATING BATH ?Bamet D. Ostrow,North 'Bellmore, N. Y.

Application November 14, 1955, Serial No. 546,584

5 Clams. (c. 20442 i The present invention is directed to cyanide copperplating baths, more particularly 'to -an improvement wherebycontaminations may be rendered harmless. The present application is acontinuation in part of my co-pending application, Serial No. -349,935,filed April 20, 1953, entitled Electroplating Compostions for Copper,now Patent 2,'732,336; and application, Serial No. 47`9,87l, filedJanuary 4, 1955, entitled Bath for Plating Bright Copper," nowabandoned.

Cyanide copper electroplating baths are commonly used in the plating ofZinc die castings and 'of steel for the purpose of depositing a copperplate prior to plating the articles with nickel and chromium. Theoperation utilizes a. plating cycle wherein the same plating racks orfixtures for holding the work pass successively through the copper,nickel and chromium baths. This practice is economical in the sense thatit is unnecessary to re-rack the articles between the successive platingbaths, but there isthe serious disadvantage that there is a tendency tointroduce a contamination by soluble salts of nickel or chromium intothe copper bath. Particles'from zinc die castings often fall into theplating bath and tend to dissolve, thereby introducng soluble zinc saltsas an impurity. In particular the high efficiency bright plating bathswhich are used extensively are particularly afiected by such solublemetallic impurities and the low efiiciency and Rochelle type baths areequally affected by chromium and zinc contaminants.

It has been proposed to remove soluble zinc mpurities by the use ofsodum sulfide when the concentration of zinc reached 0.3 oz. per gallon.Such a use has an adverse eifect as it tends to lower the bright platingrange of said bath by introducing the sulfide ion therein. In such asystem when chromium having a valence of +6 enters the cyanide copperbath in concentrations of to parts per million, very harmful sideeflects are produced, such as loss of efiiciency, decrease of coveringpower and in an extreme case, plating is totally interrupted. Theharmful efiectof the chromium is accentuated in the presence of zncsalts as impurity.

It has also been proposed to add to the cyanide copper baths sodiumhydrosulfite, in order to reduce the chromium to the harmless trivalentform, which then precipitates out. While this is somewhat efiective inprecipitating chromiun, it also introduced into the solution sulfidecompounds, such as sodum sulfide, which adversely atfected the brightplating range. With zinc present, insoluble zinc sulfides mayprecipitate and cause roughness of the deposit. It also became necessaryto make frequent additions of the hydrosulfite in quantitiesapproximately equal to the concentration of the soluble c'hromium as anexcess of hydrosulfite was harmful. y

The present invention s intended and adapted to overcome thedifiiculties and disadvantages 'inherent in prior baths of the typedescribed, it being among the objects 'of the present invention toprovide a cyanide copper bath having small amounts of additives thereinto increasethe tolerance thereof for metallic impurities andparticularly in high efficiency 'bright plating baths.

2,813,066 Patented Nov. 12, 1957 It is also among the objects 'of thepresent invention to provide a bath composition wherein suchcontaminants' as zinc, chromium and nickel may be permitted toaccumulate to a very substantal degree without detriment to the platingoperation.

It is further among the objec-ts of the present invention to introduceinto a cyanide copper bath of the usual -yPs, small amounts of additiveswithoutimpairng the eiciency of the bath and at the same timemaintaining the bright plating range thereof. i

In practicing the present invention, it has been found that thepolyamines in small amounts are very effective in increasing thetolerance of cyanide copper baths to Zinc, chromium and nickel and othermetals forming soluble complexes. The polyamines have from 2 to 6 aminogroups and each of the alkyl groupshas from l to 3 carbon atoms. Whilethe polyamines as such are preferred, it is also possible -to react thepolyamines to form condensation products which are also suitable for thepurpose.

Baths of this character have excellent tolerance for the above mentionedsoluble metallic contaminants. While they are particularly adapted tohigh efficiency baths, the beneficial efiects of such additives arefound in practically any cyanide copper bath.

`In the accompanying `drawing constituting a part here ofand in whichlike symbols indicate like deposit areas,

Fgs. I-A to I-G represent diagrammatically the results obtained in aseries of experiments for depositing copper' in a standard 267 ml. Hullcell utilizing a standard cyanide copper 'plating bath;

Figs. II-A to II-C are similar diagrammatical views showing the resultsobtained iutilizing a second standard cyanide copper bath; and

Figs. III-A to III-C are views similar to Fig. I, showing the resultsobtained using still a third standard cyanide copper bath.

In the drawings, the clear areas represent bright plating on copperstrips, and the areas having a single central horizontal line representsemi-bright areas. The crosshatched areas indicate matte deposits andthe dotubly cross-hatched areas represent burned deposits. Those areashaving a series of horizontal broken'lines are areas where no depositoccurred and the areas containing a series of crcles indicate depositswhich are discolored, being dull and black to grey. Those areas having aseries of horizontal wavy lines indicate deposits that are uneven andswirled. i

Bath No. ,I

A standard bath such as has been nsedin the prior art was utlized in aseries of comparative experiments, the bath having thefollowingcomposition:

Oz./gal. Copper cyanide '8.0 Potassium cyanide 12.7

Potassium hydroxide 5.6 Sodium thiocyanate 2.0 Cetyl-betaine .04

This bath was operated in a No. 267 ,Hull cell at F. with agitation at 2amperes for five minutes. As shown in Fig. I-A,'it`.produces a -good,bright deposit at current densties from 10 to 40 amperes per squarefoot.

To this bath there was `addedpotassium chromate in which the chromiumhas a valence of +6. The amount added .was 20 parts per million or .02grams per lter. The bath was operated as above stated, the results beingshown in Fig. "I- B. There was .a total elimination .of the 'brightareas andthere was poor coverage, particularlyin the low current density.areas.

To this bathicontaining the :potassium chromate, there was added .25`oz. per gallon *of tetraethylene pentamire and the bath was :operated,as before. As will be seen from Fig. I-C, the original characteristicsof the bath were restored so that the adverse elfect of the chromium wascompletely eliminated.

To the aforesaid standard Cyanide copper bath, there was added 75 partsper million ofchromium in the form of potassium chromate. In Fig. I-D,there is shown the results of operation with this bath, the depositsbeing striated and non-uniform in the high current density areas. Therewas no deposit in the low current density areas.

To this bath containing the chromium having a valence of +6, there wasadded .4 oz. per gallon of triethylene tetramine. The bath was operatedas before, the results being shown in Fig. I-E. The initialetfectiveness of the original bath has been completely restored. V Tothe aforesaid standard bath, there was added .5 oz. per gallon of zinein the form of Zinc Cyanide. Upon operation of the bath, the brightareas were destroyed as shown in Fig. I-F and the deposits were brass tobronze color. To this Zinc containing bath, there was added 1.0 oz. pergallon of diethylene triamine. Upon the operation of the bath as before,the brightness of deposit has been restored, as shown in Fig. I-G.

Bath No. II

Another standard bath well-known in the art is as follows:

In Fig. II-A is shown the results of a run with this bath at atemperature of l60 F. with agitation for a period of 5 minutes. Itindicates a semi-bright deposit up to 50 amperes per square foot. Tothis bath, there was added 100 parts per million of chromium in the formof potassium chromate. The results of operation of the bath are shown inFig. II-B. Little or no copper tended to deposit below 20 amperes persquare foot and the deposits were discolored, being black to grey. Atthe higher current densities, the deposits were non-uniform.

To the bath containing the chromium, there was added 1.5 oz. per gallonof triethylene tetramine. Upon the operation of the bath, the harmfulefiects of the chromium as shown in Fig. II-B were completely nullified.The bath now operated approximately as it had Originally before thechromium was added.

Bath N 0. III

Still another bath commonly used in the art has the followingcomposition:

This bath was operated in a Hull cell for five minutes ata temperatureof 140 F. As shown in Fig. III-A, the deposit was smooth, had a mattesurface up to 30 amperes per square foot and was burned above thisrange. Then there was added to the bath, 50 parts per million ofchromium in the form of Sodium chromate. The results of operation of themodified bath is shown in Fig. III-B. Little or no copper was depositedbelow l0 amperes per square foot and this had a grey to black tone. Athigh current densities, the deposit 'was nonuniform.

To the bath containing the chromium there was added 1.25 oz. per gallonof triethylene tetramine vinyl acetate reaction product. As seen in Fig.III-C, the initial efi'ectiveness of the bath was restored thereby. i

Not only the amines themselves but certain reaction products thereofwith unsaturated esters, such as vinyl acetate; aldehydes, such asaldol; and acylketones, such as acetonylacetone are effective. Suchcompounds have from 4 to 10 carbon atoms. In order to prepare suchcompounds, a mixture is made of a polyamine, vinyl acetate and water,the polyamine being tetraethylene pentamine and the proportions being 10to 15 to 75 by Volume. The reaction is exothermic and the miXture isagitated and warmed in order to cause the reaction to take place. At theend of the reaction, the mixture is heated to boiling for a few minutes.Similarly the reaction products of the other polyamines with theaforesaid compounds may be caused to take place.

In another aspect of the invention, the contamination of a bath withchromium may be reduced by precipitating the chromium compound even inbaths containing tartrates or similar radcals. As an example, apolyamine or its reaction product as set 'forth above is added to thebath. It is then treated with a small amount of an alkaline earth suchas calcium or magnesium hydroxides or calcium oxide. This results in aprecipitation of the chromium compound having a valence of +6.

In Operating this phase of the invention, the Bath No.- II, which iscontaminated With parts per million of chromium having a valence of +6,is held at a temperature of to F. for about one hour in the presence of1-2 oz. per gallon of lime. The precipitated material is allowed tosettle and is filtered off. About 80% of the chromium present is thusremoved. An examination of the filtered precipitate under a spectregraphshows that the chromium has been adsorbed on the alkaline earth by thistreatment.

The concentration of the polyamine or its reaction product may vary from.Ol to 50 grams per liter. The lower limit used depends upon theconcentration of the metallic impurities which are to be nullified. Alarge excess of the polyamine or its reaction product has no undesirableeflect on the piating characteristics of the bath. By this invention,impurities up to 200 to 250 parts per million may be tolerated, whereas5 or 10 parts per million of such impurities in the standard baths madesuch baths practically unworkable for plating bright copper.

The polyamines and their reaction products are capabe of formingcompiexes with various bath impurities other than zine, chromium andnickel, thus scquestering them. Still higher nolecular weight polyaminesup to a molecular weight of about 2000 are capable of use in accordanceWith the invention with good results.

What is claimed is:

l. A method of treating Cyanide Copper plating baths having therein freealkali metal hydroxide and containing soluble contaminants taken fromthe class consisting of Zinc, chromium and nickel which comprises addingto said bath an unsubstituted alkylpolyamine in sufcient amount tosequester said contaminants, said amine having 2 to 6 amino groups andthe alkyl groups each having 1 to 3 carbon atoms.

J 2. A method of treating cyanide Copper plating baths having thereinfree alkali metal hydroxide and containing soluble contaminants takenfrom the class consisting of Zinc, chromium and nickel which comprisesadding to said bath an unsubstituted alkylpolyamine in suicient amountto sequester said contaminants, said amine having 2 to 6 amine groupsand the alkyl groups each having 1 to 3' carbon atoms, the concentrationof said polyamine being from .01 to 50 grams per liter.

3. A method of treating cyanide Copper plating baths having therein freealkali metal hydroxide and containing soluble contaminants taken fromthe class consistng of Zinc, chromium and nickel which comprises addingto said bath an amine selected from the group consisting ofunsubstituted alkylpolyamines and alkylpolyamine compounds in sufiicientamount to sequester said contaminants, said amine having 2 to 6 aminegroups and the alkyl groups each having l to 3 carbon atoms, said.

compound' being a reaction product of said a1ky1polyamne with a compoundtaken from the class consisting of unsaturated esters, unsaturatedaldehydes and unsaturated acylketones having 4 to 10 carbon atoms.

4. A method of treating Cyanide Copper plating baths having theren freealkali metal hydroxide and containing soluble contaminants taken fromthe class consisting of Zinc, chromium and nickel which comprises addingto said bath an unsubsttuted alkylpolyamine having 2 to 6 amino groupsin sufficient amount to sequester said contamrants, said amine having amoiecular Weight up to about 2000, and the alkyl groups thereof having 1to 3 carbon atoms.

5. A method of treatng Cyanide copper baths having therein free alkalimetal hydroxide and containing soluble contaminants capable of formingcomplexes with polyamines which comprises adding to said bath anunsubstituted alkylpolyarnine having 2 to 6 amino groups in suflicientamount to sequester said contaminants, said amne having a molecularweight up to about 2000, and the alkyl groups having 1 to 3 carbonatoms.

References Cited in the file of this patent UNITED STATES PATENTS2,195,454 Greenspan Apr. 2, 1940 2,434,191 Benner et al. Jan. 6, 19482,582,233 Chester et al. Jan. 15, 1952 2,660,554 Ostrow Nov. 24, 19532,662,853 Ellis Dec. 15, 1953 FOREIGN PATENTS 694,893 Great Britain July29, 1953 OTHER REFERENCES Versenes: Bersworth Chem. Co., Framingham,Mass., pp. 46-8, sec. II February 1952.

Gilbertson et al.: Transactions of Electrochem. Soc., vol. 79, pp.439-442, 1941.

1. A METHOD OF TREATING CYANIDE COPPER PLATING BATHS HAVING THERIN FREE ALKALI METAL HYDROXIDE AND CONTAINING SOLUBLE CONTAMINATS TAKEN FROM THE CLASS CONSISTING OF ZINC, CHROMIUN AND NICKEL WHICH COMPRISES ADDING TO SAID BATH AN UNSUBSTITUTED ALKYLPOLYAMINE IN SUFFICIENT AMOUNT TO SEQUESTER SAID CONTAMINANTS, SAID AMINE HAVING 2 TO 6 AMINO GROUPS AND THE ALKYL GROUPS EACH HAVING 1 TO 3 CARBON ATOMS. 